INTRODUCTION. . 23 rea hot and pmnged in water the carbon in the metal unites with the iron in some peculiar way so as to produce a compound of extreme hardness. If the steel contain one-third of one per cent, of carbon a sharp point so quenched will scratch glass. With two-thirds of one per cent, the steel is hard enough to- make common cutting tools. With one per cent, it reaches nearly its limit of hardness. This percentage is used for the harder tools, but with higher carbons the brittleness increases so fast that the usefulness of ther metal is limited. Nickel: This element in alloy with-steel gives a metal with a high elastic limit and having great toughness under shock. Its principal uses are for armor plate and special forgings. Chapter XYII describes two investigations I have made into the influence of the metalloids. The first was by the Method, of Least Squares and the second by plotting. The formula? deduced were as follows: First Method: A. Acid Steel 38600+1210C+890P-f-E=Ultimate Strength. B. Basic Steel 37430+950C+85Mn+1050P+E=Ultimate Strength. Second Method: C. Acid Steel 40000+1000C+1000P+XMn-|-E=Ultimate Strength. D. Basic Steel 41500+770C+1000P+YMn-f-E=Ultimate Strength. In equations C and D the factors X and Y are variables, being zero in a low steel, but rising with each addition of carbon and manganese. In these equations the contents of carbon, manganese and phosphorus are to be given in units of .01 per cent., while E is a factor depending upon the finishing temperature, and it may be plus or minus. The results indicate that the metalloids have different quantitative effects upon acid and basic steels. Now, if acid steel does not follow the same law as basic steel, then they are not the same, and if they are not the same, then it is possible that one is better than the other, a possibility that is vigorously denied by some people.